Tunable lasers are used in a variety of applications, such as optical test sets for measuring wavelength-dependent characteristics of optical devices and in optical test instrumentation. In optical heterodyne systems, swept tunable lasers are typically used as the local oscillator. The optical output of the local oscillator is combined with the optical test signal in an optical mixer, and the resulting intermediate frequency is measured. The wavelength of the optical test signal is calculated from the intermediate frequency and the frequency of the local oscillator. Thus, it is important to track the wavelength of the local oscillator. Unfortunately, swept tunable lasers that sweep continuously over a wide spectral range are expensive. Less expensive swept tunable lasers are available, but sweep over a narrower spectral range before mode hopping. Mode hopping generally occurs when the lasing mode suddenly changes, and results in a discontinuity in the output wavelength from the laser that interferes with wavelength tracking.